The use of closed recirculating water reservoirs for use by the general public, for example, swimming pools, spas, hot tubs, decorative fountains, cooling towers and the like, has led to a variety of water quality problems. For instance, improper chemical balances in the water can lead to various types of contamination including bacterial and viral contamination.
The use of chemical oxidizers/sanitizers is a fairly standard water sanitation method. Addition of so-called halogen donor compounds, such as chlorine and bromine are effective sanitizers so long as they are maintained at well defined and constantly controlled concentration levels in the water. It is important that the concentration of these chemical sanitizers is not allowed to become too high which may cause irritation to the users and damage to the water system. Insufficient sanitizers result in a contaminated condition.
The difficulties in maintaining a proper balance of sanitizers may arise from numerous load factors that are difficult, if not impossible, to predict. For instance, in a pool the load factor is typically caused by varying numbers of users. In hot tubs the use of air jets and high water temperatures tend to destroy or remove the sanitizer from the water. Cooling towers are subject to environmental conditions, such as fluctuations in temperature. Indoor decorative fountains may be affected by the air quality in the building, while the fountain water can also affect the air in the building.
Various testing devices exist for determining the chemical balance of the water of pools, spas and the like, for example, colormetric chemical test kits are available that utilize liquid droplets, test strips or tablets which dissolve in the water to indicate a particular level or concentration of sanitizing agents. By removing a test sample of water, for example via a scoop or cup, a seemingly representative sample is deemed to have been taken. A staining agent is then added by means such as an eye dropper or the like. The degree of staining relates to the amount of sanitizer in the water. The amount of sanitizer present is determined by visually comparing the degree of coloring of the test sample against a test scale previously formulated. Further complicating the task of maintaining sanitary conditions in such bodies of water is the fact that studies now indicate there is little correlation between the free halogen, e.g. chlorine, residual readings which are normally used to monitor such bodies of water and the actual bacteriological quality of the reservoirs themselves. Pool and spa maintenance officials have long gone under the assumption that maintaining a free chlorine residual of two milligrams per liter or two parts per million will insure a safe water condition. Thus, the parts per million reading which is determined via the stain comparison, is actually a reflection of the sum of the free chlorine and combined chlorine compounds such as chloramine which are present in the water. These combined chlorine derivatives do not protect from bacteria and/or viral contamination. Additionally, since organic and chemical loading drastically reduce the ability of free chlorine to overcome bacteria, the available free chlorine test kits are of questionable value unless the exact levels of organic contaminants and the particular pH of the water being tested is known.
U.S. Pat. No. 4,752,740 suggests the use of monitoring the oxidation-reduction potential (ORP) as a method of measuring the sanitization levels of water. ORP defines the potential of a sanitizer such as chlorine, bromine or ozone to react with various contaminants. These compounds are known as oxidizers and have the property of "burning off" impurities in the water, for example, body wastes, algae and bacteria. The use of an ORP sensor allows the pool maintenance engineer to measure the potential generated by the active form of the sanitizer and not the inactive forms such as the combined chlorine derivatives. Additionally, ORP monitoring has an advantage in that it is an ongoing electronic process requiring no test chemicals or agents and monitoring of sanitation levels is constantly performed as opposed to being performed on some predetermined schedule basis. Since the potential for disease transmission due to organic loading is far more significant in public spas and pools, use of ORP measurement could be of great benefit in reducing the risk of contamination and disease transmission.
In accordance with standards set forth by the World Health Organization in 1972, maintenance of an ORP level of 650 millivolts is deemed to result in a water supply that is disinfected and in which viral inactivation is virtually instantaneous.
Chlorine is the most widely used oxidizer in the aquatic industry, the primary use being for sanitation of the water in pools and spas. Chlorine, being an oxidizer, is also involved in oxidation reactions with organic and nitrogen based substances such as urea, uric acid, amino acids etc. One of the drawbacks of chlorine is the production of chlorinated by-products which produce undesirable side effects such as irritation of the eyes, sinuses, skin, foul smelling air, and corrosion of air handling equipment.
Numerous attempts have been made at addressing this problem. "Shocking" of the pool water requires dosing the water with stoichiometric concentrations of chlorine to oxidize these substances. One problem with this method is that there cannot be any bathers present due to the excessive concentrations of chlorine required to meet the stoichiometric levels needed when the undesirable substances have been allowed to accumulate. Another issue this method addresses is the problem after the symptoms have appeared (i.e., high combined chlorine, foul odors, etc.). Also, in many cases this method fails to rid the water and air of these substances since the concentration of chlorine required is at best a rough estimate (incorporates measuring the combined chlorine in the water). Measuring the concentration of combined chlorine in the water does not take into consideration the accumulated demand that is non-aqueous, e.g. accumulated on the filter media, walls of the pools, etc. As the chlorine levels rise, some of this accumulated demand is liberated, thereby preventing the chlorine from reaching the necessary stoichiometric levels. This prevents the water from reaching "breakpoint".
Ozone has been used as a side stream treatment to destroy these undesirable substances. While it is an effective sanitizer, ozone cannot be applied to the bulk water of the pool where the contaminants are being added. Furthermore, since ozone cannot maintain a residual concentration in the body of water, it cannot be used as a stand-alone treatment, chlorine or bromine is used as the primary sanitizer. Besides being expensive and often requiring extensive de-ozonation equipment, e.g. as activated carbon, ozone destroys chlorine by attacking the hypochlorite ions, thereby further increasing operational and maintenance cost.
Bromine is sometimes used in place of chlorine because of the belief that it does not produce the air fouling by-products produced by chlorine. However, while bromamines are not as volatile as chloramines, they do possess an odor and irritate the eyes. Bromine also requires an oxidizer such as chlorine or ozone to activate the bromide ion. Operating costs tend to be high and it is often difficult to maintain water quality since no easy methods are available for differentiating between free or combined bromine. Also, hydantoin, an additive commonly used to pelletize the bromine chlorine combination, reduces the oxidizing power of the bromine as the hydantoin accumulates in the water. This makes it more difficult to reduce the accumulation of undesirable brominated compounds.
ORP is a qualitative measurement of the oxidation or reduction power and has been used in aquatics since 1972 when the Stranco Company introduced these systems to the industry. Despite the use of ORP controllers, the varying load factors are difficult to instantly react to and the control of air and water quality continues to be a problem at indoor aquatic facilities.
While ORP has been established as the primary indicator for determining the inactivation rates of various bacteria and viruses, dosing aquatic water with part per million (PPM) measurement of chlorine has been the accepted method used for meeting the oxidation needs of aquatic facilities. For example, while 650 mv is commonly used as the minimum required oxidation potential to ensure sanitized conditions in a pool or spa, the health departments nevertheless requires PPM levels of chlorine.
Despite maintaining health department levels of chlorine and/or operating with ORP levels in excess of 650 mV, following prescribed methods of superchlorination (breakpoint chlorination) as described on the product literature and in the "Certified Pool Operators" (CPO) training course, the problems resulting from incomplete oxidation are widespread.
Thus, if a method could be devised for reducing or eliminating impurities present in the air and water associated with aquatic facilities while maintaining the required levels of sanitization, a longfelt need would be realized.